Paper coating method employing high flexible blade pressures



Nov. 24, 1964 H. 5. FIRD ETAL 3,158,497

PAPER comma METHOD EMPLOYING HIGH FLEXIBLE BLADE PRESSURES Filed Aug.17, 1961 2 eets-Sheet 1 1-1. G FVIRD ETAL 3,158,497

Nov. 24, 1964 PAPER COATING METHOD EMPLOYING HIGH FLEXIBLE BLADEPRESSURES 2 Sheets-Sheet 2 Filed Aug. 17, 1961 \u 36 In A 3 I! Q is .7,A" .1 I I I I Wil 2 HI" 22 1 I E I? /i agA' United States, Patent()fitice 3,158,497 Patented Nov. 24, 1964 3,158,497 PAPER QGATING METHODEMPLGYENG HIGH FLEXIBLE BLADE PRESSURES Harold G. Fird, Kimberly, Wis,and Herman B. Iiustice, Center-ville, Ohio, assignors to Kimberly-ClarkCorpo ration, Neenah, Wis., a corporation of Delaware Filed Aug. 17,1951, Ser. No. 132,036 1 Claim. (1. 111-102) This invention relates tothe application of coating materials to traveling paper webs and isparticularly directed to the coating of relatively heavy papers of about60 pounds basic weight and above for the purpose of improving thesurface character of such papers.

In the coating of paper webs, compositions which are essentially aqueousfluid suspensions of pigment and adhesives are commonly employed. Incertain desirable modes of application of such coatings, usually termedmineral coatings, an excess of the coating material is furnished the weband a flexible blade is used to trowel or smooth the coating onto thepaper, the excess being removed by the blade. Occasionally hardparticles of such a com position, or particles of foreign material, arecarried with the coating composition to the area of contact of the bladeand paper. The lodging of such particles between the blade and paperthen may result in marking or scratching of the coating on the web; inextreme cases the web may even be torn as it passes beneath the blade.

Such web is, in practice, carried to the flexible blade on a backingroll having a somewhat resilient surface. Pressure is applied to theblade and its holder to maintain the blade in contact with the web andcoating composition. Such pressure is generally low and adequate wei htsof coating on the web are attained with coating compositions of a solidscontent of 50-55%.

We have found that the surface characteristics of such paper may bematerially improved, particularly with relation to the tendency of thecoating to scratch or streak, by materially increasing the pressure ofthe blade against the traveling web. In addition, we have found thatwhile the increased pressure tends to decrease the coat weight achievedwith a coating formulation of given solids and viscosity, thecomposition solids may be increased to procure desirable coat weightwithout occasioning the coating to acquire surface imperfections, andwhile attaining a smooth surfaced uniform thickness paper sheet.

Accordingly, a primary object of this invention is to provide a novelprocess for the application of mineral coating materials to travelingpaper webs.

The invention may be practiced by the utilization of many differentmechanical constructions and, therefore, the arrangement set forth inthe accompanying drawings is to be regarded as illustrative only and forthe purposes of more clearly setting forth the features of theinvention.

Other objects and advantages obtained by our process will becomeapparent from the drawings wherein:

FIG. 1 is a view showing the cooperation between the blade, paper weband backing roll, and the coating composition supply in a preferredembodiment of the invention.

FIG. 2 is a perspective view of one structural arrangement for thepractice of the invention;

FIG. 3 is a side elevational view of the structure of FIG. 2; and

FIG. 4 is a view taken on line 4-4 ofFIG. 3.

In the drawings corresponding parts are designated by similar numeralswhere such is appropriate.

Referring to the drawings, the numeral 1 designates a longitudinallyextending backing roll which suitably has a diameter of about 30 inchesand is arranged to be driven or, more specifically, web contact.

ball has a density of 56; suitably, in the practice of the inventionthis density may lie in the range of 47 to 70.

An applicator roll 3 is coextensive longitudinally with the backing rolland is in rotatable contact with metering roll 7; the applicator roll 3is supplied through the metering train rolls 7 with coating compositionfrom pond 5. Pond 5 may itself be supplied with coating compositionthrough nozzle means, one of which is shown at 4. Applicator roll 3 isarranged to be driven in counter rotation to the roll 1 as indicated bythe arrow. A nip 6 is formed between the applicator roll and the backingroll.

A web of paper 8 is passed continuously to the nip 6 in the practice ofthe invention. Coating composition in excess, in the form of a heavyfilm, is applied to the traveling web at the nip and the coatingcomposition is carried upwardly on the web in the rotation of thebacking roll toward the flexible knife blade 1%.

Blade 10 is of tempered steel, has a thickness of about 0.012 inch, andis honed at its tip; the blade in practice is flexed somewhat by appliedpressure.

The blade 10 is supported in a blade holder 12 which is itself securedby bolts as at 14 to a mounting i6. Mounting 16, as shown, is triangularin form and composed of three longitudinally extending bars or panels; aplate 18 is welded to each end of the mounting closing the ends. Eachplate 18 is also welded to a shaft 29 thereby rigidly fixing the shafts20 to the mounting. Accordingly, rotation of shafts 20 causes themounting 16, blade holder 12, and blade 10 to rotate relative to thebacking roll 1.

For the purpose of rotating shafts 25), a link 22 is secured to eachshaft and is itself secured to a pin as at 24. Pin 24 forms a lowerextremity of the flexible joint 26 which at its upper end is secured tothe piston rod 28 of an air cylinder 30. Thus air pressure applied tothe cylinder 30 depresses the link 22 and rotates the shaft 20 towardthe backing roll, applying 10.

The shaft 29 is supported by bearing blocks 32 on each side of themounting 16. A frame 34 supports each hearing block; each frame isitself supported from the bed plate 36 of the roll-bearing housing 358.Frame 34 is apertured on each side at 39 to provide for the passage ofshafts 2d.

Bearing housing 38, one on each side of the machine, carries the roll 1.The blade is thus well supported for pressure application.

Blade pressure as referred to hereinafter and in the ap: pended claimsis set forth as the radial load in pounds per lineal inch imposed by theblade on the roll. More specifically, it is the force per lineal inch inthe direction of the radius of the backing roll at the line ofblade-roll The direction of this force and the radius are designated bythe arrow and letter R respectively in FIG. 1.

Commonly, in usual practice, this bladepressure is low-on the order ofone or two pounds per lineal inch. With basis weight Webs of 60 poundsand above, such pressures, utilizing a composition having a solidscontent of approximately 57-59% and a composition viscosity in the rangeof 50 to poises, yields a coating weight on one side of the web of 89pounds, with the web speed on the backing roll at about 600-700 feet perminute. For this purpose it is only necessary that the mechanismapplying the coating to' the websuch as applicator roll 3furnish thecoating composition in excess.

pressure to the blade We have found that marks induced in the finishedcoatmaterially minimized by increasing the pressure of the blade severalfold-to at least 6.5 pounds per lineal inch, without other change in theoperation. Such pressure corresponds to very high pressures per squareinch since the blade area in contact with the web is low. For example,with a contact length on the roll periphery of 0.020 inch the pressureexceeds 300 pounds per square inch at 6.5 pounds per lineal inch.

In general, it is preferred to maintain the pressure be tween about 6.5to 9.0 pounds per lineal inch of blade pressure exerted radially of theroll in order to achieve substantial blade mark elimination.

Such pressure does tend to reduce the weight of coating applied.However, we have further found that the coating weight may be maintainedif the solids content of the coating is increased also-and that suchhigher solids content may be employed while retaining the beneficialeffect of the higher blade pressures as to the blade marks.

The solids content, in the invention as practiced, is correlated withthe blade pressure to achieve the desired coat weight. Thus, a solidscontent of the coating composition, while maintaining viscosity in thegeneral range indicated, of about 60-64% solids, permits the attainmentof coat weights per side in the 8-9 pound range.

By way of specific example: a paper web as at 3, having a basis weightof 70 pounds and absorptive to the fluid coating, is continuously formedon the paper machine and in the customary manner dried and passed to thenip 6; such web normally, on entering the nip, has a low moisturecontent of about 46%, dependent to some extent upon ambient temperatureand humidity conditions.

The composition 5 contains in parts by weight:

Clay 70 Calcium carbonate 30 Starch 19 Sodium hexarnetaphosphate 0.2Caustic 0.2 Calcium stearate 0.5 Soap 0.5 Watersufiicient to provide 61%solids 77 The viscosity of this formulation is 60 poises; it is to beunderstood, however, that the viscosity may vary somewhat dependent uponthe specific conditions of the materials used, as is known in the art,and the practice of the invention is not adversely afiected by variationof viscosity within the limits indicated-that is, 50 to 80 poises.

This coating composition is carried in the travel of the web to theblade. The blade holder extends at an angle of about 55 to the tangentto the backing roll at the point of blade contact (FIG. 1); the bladeitself projects about /1 inch beyond the holder and suitably is ofspring steel of a thickness of about 0.012 inch. The blade thicknessshould not exceed 0.024 inch and, in fact, is somewhat too stiff at thisthickness with a inch projection.

Such composition as described when applied to the 70 pound basis weight(25" x 38" x 500 sheets) web 8 (FIG. 1) results in a coating weight of8-9 pounds per web side when the web speed is about 650 feet per minuteand the blade pressure is 6.5 pounds per lineal inch.- The web itselfhas some effect on the weight pickup and in some instances of webcondition 10 pounds per side may be achieved. However, with the samecomposition, but in creased water content to give lower solids of about56%, a coat weight of roughly 5-6 pounds per side is attained at thesame blade pressure. The lower weight pickup in some instances is notdetrimental but generally, in the production of bookpaper, higher coatweights are desired to provide an improved printing surface. In eitherevent blade scratches are minimized and the customarily desired coatweights are achieved and the printing character of the coatingdetermined by correlating the solids content of the composition with thehigh blade pressures.

At higher blade pressures of about 9.5 pounds per lineal inch the coatweight-tends to drop slightly; accordingly, it is preferable to maintainthe composition solids at the high end of the -64% range with thishigher blade pressure.

It will be understood that this invention is susceptible to modificationin order to adapt to different usages and conditions and, accordingly,it is desired to comprehend such modifications within the invention asmay fall within the scope of the appended claim.

What is claimed is:

In a process for the production of coated paper in which a travelinguncoated, absorptive paper web is coated with an aqueous mineral coatingcomposition which is subject to the inclusion therein of scratchproducing particles and which web is continuously drawn in the coatingprocess on a resiliently covered rotating backing roll from a firstpressure nip formed between the resiliently covered backing roll and adriven applicator roll to a second pressure nip formed between the saidbacking roll and a flexible blade having a thickness of between about0.012 and 0.024 inch, the steps of:

(a) driving the said backing roll and said coating applicator roll incounter-rotation and in the direction of web travel;

(12) applying to said web with said applicator roll an excess of theaqueous mineral coating composition having a viscosity of 50 to poisesand a solids content of about 60 to 64 percent by weight, said webhaving a basis weight (25" x 38" x 500 sheets) of at least about 60pounds;

(c) passing the said web on said backing roll to said second pressurenip formed by said flexible blade and said backing roll at a positionspaced 6 round the backing roll from the first pressure nip; and

(d) pressing said blade into contact with said web on said roll surfaceto trowel excess of coating composition from the web, to smooth theremainder of coating composition on the web and produce a pressureradially of the backing roll on the web of between about 6 /2 to 9pounds per inch over the length of blade contact with the web, saidpressure being at least 300 pounds per square inch andwhich square incharea is based on the area of contact of the blade with the web.

OTHER REFERENCES -Heiser: Paper Coating Trends in the United States,Svensk Pap-pars Tidning (Swedish Paper Journal), pp. 389 et seq., June30, 1958.

